R help - Oct 2012 - anova test for variables with different lengths

Hi all,

I want to test whether the MEAN of two different variables, (and
different number of observations) are the same. I am trying to use the
anova test but it doesn't seem to like that the number of observations
are different:

a=c(1:5)
b=c(1:3)
aov_test=aov(a~b)
>>Error in model.frame.default(formula = a ~ b, drop.unused.levels = TRUE)
:
  variable lengths differ (found for 'b')

Any ideas as to how I would go about doing this test?

Thanks,
Sachin

Hi Sachin,

You may find this tutorial useful:
http://goanna.cs.rmit.edu.au/~fscholer/anova.php
And you'll need the car package; but become yourself familiar with Type I,
II and III sums of squares models before running the Anova; the tutorial
explains these in detail.
Hope it helps.

Jos?


Jos? Iparraguirre
Chief Economist
Age UK

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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Sachinthaka Abeywardana
Sent: 16 October 2012 04:18
To: r-help at r-project.org
Subject: [R] anova test for variables with different lengths

Hi all,

I want to test whether the MEAN of two different variables, (and
different number of observations) are the same. I am trying to use the
anova test but it doesn't seem to like that the number of observations
are different:

a=c(1:5)
b=c(1:3)
aov_test=aov(a~b)
>>Error in model.frame.default(formula = a ~ b, drop.unused.levels = TRUE)
:
  variable lengths differ (found for 'b')

Any ideas as to how I would go about doing this test?

Thanks,
Sachin

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